Submitted to: National Research and Action Plan for Silver Leaf Whitefly
Publication Type: Abstract Only
Publication Acceptance Date: January 10, 2000
Publication Date: N/A
Technical Abstract: A system of markers designed to track the development of fourth instar greenhouse whiteflies has been used to track the development of fourth instar silverleaf whiteflies. The system is based on the measurement of body depth and observed changes in the size and color of the developing adult whitefly eye. Stages 0, 1, 2, 3, 4, and 5 have body depths of less than 0.1, 0.1, 0.15, 0.2, 0.25 and 0.27-0.30 mm, respectively. Stages 6, 7, 8, and 9 are characterized by slightly diffuse eye pigmentation, a light red, bright red bipartite and red-black bipartite eye, respectively. Since adult eye development is first observed in stage-6 fourth instars, it was hypothesized that molting (i.e., apolysis, the separation of the larval cuticle from the epidermis) occurred shortly before this stage. Histological studies revealed that for the greenhouse whitefly, adult wing and eye development do begin in stage-5 fourth instars. Metamorphosis is rapid during stage 6. Since in other insect orders an increase in ecdysteroid levels has been found to be associated with the molt, an Enzyme Immunoassay was used to determine whole body ecdysteroid (molting hormone) titers in staged greenhouse and silverleaf whiteflies. For the greenhouse whitefly, mean whole-body ecdysteroid titers fluctuated between 0.068 and 0.34 pg/whitefly. For the silverleaf whitefly, titers fluctuated between 0.079 and 1.35 pgs/whitefly. Thus, at peak periods (occurred in stage-5 greenhouse and stage 4/5 silverleaf whiteflies), the ecdysteroid titer in fourth instar silverleaf whiteflies is approximately four times greater than the titers in greenhouse whiteflies. It is noteworthy that whole-body ecdysteroid levels of last instar whiteflies are considerably lower than those reported for last instars of other insect orders.